Selective and irreversible adsorption of mercury(ii) from aqueous solution by a flower-like titanate nanomaterial

Abstract

A novel flower-like titanate nanomaterial (titanate nanoflowers, TNFs) was synthesized through a hydrothermal method using nano-anatase and sodium hydroxide, and used for mercury(II) removal from aqueous solution. The large surface area (187.32 m² g⁻¹) and low point of zero charge (3.04) of TNFs facilitated the adsorption of cations. Adsorption experiments indicated that TNFs could quickly capture 98.2% of Hg(II) from solution within 60 min at pH 5. The maximum adsorption capacity of Hg(II) was as large as 454.55 mg g⁻¹ calculated by the Langmuir isotherm model. Moreover, selective adsorption of Hg(II) by TNFs was observed with the coexistence of other conventional cations (i.e., Na⁺, K⁺, Mg²⁺ and Ca²⁺) even at 10 times concentration of Hg(II). XRD analysis indicated that the prepared TNFs were a kind of tri-titanate composed of an edge-sharing triple [TiO₆] octahedron and interlayered Na⁺/H⁺, and ion-exchange between Hg²⁺ and Na⁺ was the primary adsorption mechanism. Furthermore, it was interesting that the basic crystal structure of TNFs, tri-titanate (Ti₃O₇²⁻), transformed into hexa-titanate (Ti₆O₁₃²⁻) after adsorption, resulting in the trapping of Hg(II) into the lattice tunnel of this hexa-titanate. Desorption experiments also confirmed the irreversible adsorption due to Hg(II) trapped in TNFs, which achieved safe disposal of this highly toxic metal in practical application.